I can say for the MY1998 986 it's relatively easy:
- Remove six to eight various philips or torx or hex screws around the lower lip of the bumper. The outer pair are tucked up just near the top/end of the bumper panel in the wheel well. You may have more or fewer screws, and of different types, depending on work done by other mechanics....
- Raise the spoiler. Open the trunk.
- Push the pin thru the center of the 3 plastic rivets on the leading edge of the spoiler. You'll have to retrieve them later so be careful when you do move the spoiler 'cause they're inside and can fall out and get lost.
- With the pins pushed thru, now pull the rivets out. You'll have to carefully pry around the edges with something thin.
- Gently but firmly pry around the painted spoiler top panel lip with your fingers to remove it. Try wiggling the leading edge up, then prying up around the trailing edge and corners. It's being held by little plastic protrusions built into the trailing edge lip.
- Using a strong arm on a screwdriver with a (6mm?) hex bit, reach into the hole at each end of the spoiler top and remove the two bolts that hold the spoiler to the up/down poles. Strong because there is loctite on these bolts!
- Now put the spoiler aside (recover those 3 rivet pins as they spill out).
- You can probably get away with just loosening one of the two spoiler bolts, and pivoting the spoiler around on it, resting it on the trunk weatherstripping.
- Remove the 3 philips head screws that are now reachable that hold the top of the bumper to the car.
- Remove the bumper. You'll probably have to unplug the license plate light wire if you want to put the bumper all the way down on the ground. You can pull more slack thru the grommet on the left if it helps. The connector is near the grommet, not near the license plate lights.
So: several screws around lower edge of bumper; remove spoiler (plastic rivets, painted cap, main bolts) to access three screws on top edge of bumper; license plate light wire.
For the Spec Boxster I would like to figure out a way to undo those three upper bumper screws without removing the spoiler. Perhaps drilling three access holes in the spoiler and taping over them.